348 WHITMAN CROSS 
rocks, Yet von Leonhard did not give his science a name, and 
presents itasa part of geognosy. 
Von Leonhard says that his object is to present all facts 
bearing upon the character of rocks, an aim expressed in his 
chosen title. He points out that a discussion of the stratigraphic 
relations of rocks must be preceded by an accurate statement of 
their nature. Rocks are defined as the mineral masses of more 
or less considerable extent in the crust of the earth. It is 
recognized that, from the standpoint of geognosy proper, only 
those masses can be considered important the extent of which 
is so considerable that general laws as to their relations and 
distribution may be discerned. Yet it is pointed out that there 
are other masses of subordinate or abnormal occurrence which 
may have a wide distribution, though occupying no position 
peculiar to themselves, and that these masses are important 
when arranged by their characteristics. Stratigraphic geology 
and petrography are thus fairly outlined, though no definite pro- 
posal for their separation is made. 
The classification presented by von Leonhard has many fea- 
tures which are preserved in modified form in the German sys- 
tems of today. Like all early systems, however, the primary 
division is arbitrary, and drawn upon no definitely stated prin- 
ciple. Four divisions are established : (1) Heterogeneous rocks, 
(2) Homogeneous rocks, (3) Fragmental rocks, (4) Loose rocks, 
while coals are placed in an appendix. For subdivision, structure 
is used as the basis, the granular, schistose, porphyritic, dense, 
and glassy groups being established in some of the main divi- 
sions. These terms are used with nearly the meaning we now 
attach to them. The principal anomalies of association in the 
arrangement arise from the throwing together of igneous and 
sedimentary rocks in certain groups, and from the inconsequent 
way in which von Leonhard met the difficulty of dealing with 
the more or less dense rocks, the composition of which could 
not then be ascertained. These were mainly of igneous origin, 
and not stratigraphic units, and there was no proper place for 
them in the system. They were treated as a group by them- 
